1. Field of the Invention
The present invention relates to using a fluid-bed catalyst for the preparation of ethylene and propylene by catalytic cracking, and in particular, using a fluid-bed catalyst for the preparation of ethylene and propylene by catalytically cracking naphtha.
2. Description of Background Art
Currently, steam thermocracking is the most popular method for preparing ethylene and propylene, and naphtha is the raw material used most frequently. However, steam pyrolysis of naphtha has the disadvantages including a high reaction temperature, strict process conditions, high requirements for devices, especially furnace pipe materials, a large amount of CO2 that is released and big loss. It has become an issue attracting more and more attention to seek a suitable cracking catalyst, which does not effect the above disadvantages.
In the patents U.S. Pat. Nos. 4,620,051 and 4,705,769 of Royal Philips Electronics (US), an oxide catalyst comprising manganese oxide or ferric oxide as the active component, the rare earth element La and the alkaline earth metal Mg is used for cracking C3 and C4 raw materials. The Mn,Mg/Al2O3 catalyst is put in a fixed-bed reactor in a laboratory, the temperature is 700° C., the mol ratio of water to butane is 1:1, the butane conversion may reach 80%, and the ethylene and propylene selectivities are 34% and 20%, respectively. It is alleged in said two patents that naphtha and fluid-bed reactors are also usable.
The patent CN1317546A of Enichem SPA (IT) relates to a catalyst of the chemical formula 12CaO.7Al2O3 for steam pyrolysis reactions. The raw material may be naphtha, the operational temperature is from 720 to 800° C., the pressure is from 1.1 to 1.8 atm, the contact time is from 0.07 to 0.2 second, and the ethylene and propylene yield may reach 43%.
In the patent USSR Pat1298240.1987 (USSR), Zr2O3 supported on a pumacite or ceramic is used, the temperature is from 660 to 780° C., the space velocity of the moderate device is from 2 to 5 h−1, the weight ratio of water to naphtha is 1:1. The raw materials are N-paraffin C7-17, cyclohexane and straight gasoline, the ethylene yield may reach 46% and the propylene yield may reach 8.8%.
The patent CN1480255A (CN) introduces an oxide catalyst for the preparation of ethylene and propylene by catalytically cracking the raw material naphtha at a temperature of 780° C., wherein the ethylene and propylene yield may reach 47%.
To sum up, the current technology of preparation of ethylene and propylene by catalytic cracking requires a relatively high reaction temperature, but the yields of ethylene and propylene are not remarkably increased.